What 30-minute workout offers the best results?

Personal trainer

Every workout should start with a low-level aerobic activity that involves the muscle groups to be targeted during that session. You might walk quickly on a treadmill or use an elliptical trainer for five to ten minutes. Because stretching is actually pretty demanding on the muscle tissue, it should only be done once muscles are warmed up. Core training should also be incorporated into everyone's routine, because it helps maintain stability, balance, and coordination. This means doing sit-ups or using a balance ball or band to target the lower back.

In terms of gaining muscle strength and burning fat, a circuit routine is ideal. Pushing, pulling, and squatting should form the foundation of your workout. Any exercise in which you use your upper body to pull toward your torso — such as rowing or lat pull-downs — is a good pulling exercise. Doing push-ups is a good pushing exercise, and a leg press is good for squatting. When these are performed at a higher rep range (about 20 to 25 reps), you deplete energy in the muscles enough so that when you're eating or sleeping your body is actually burning fat to replace this lost energy. -Ron J. Clark, president, National Federation of Professional Trainers, Lafayette, Indiana

Cardiologist

We're learning more every day about how exercise helps the cardiovascular system. Research shows that exercise improves the function of vessels, helping them dilate and bring more blood and oxygen to tissues. Strength (resistance) training, as well as endurance (aerobic) training increase the muscle mass of the heart.

Incorporating 30 minutes of an aerobic activity into your workout is key; you should be striving to raise your heart rate to at least 60 percent of your age-predicted maximum heart rate, which you can figure out by subtracting your age from 220. [For example, if 160 beats per minute is the maximum heart rate for a 60-year-old, that person's heart rate should stay around 98.] Any exercise that raises your heart rate and gets you breathing hard and sweating is good — running, bicycling, swimming, or stair climbing.

For low-impact aerobic exercise, I recommend a treadmill inclined to its maximum — usually 15 degrees. Just a brisk walk at this incline will make you sweat (don't hold onto the handlebars, though, that's cheating). I usually recommend that someone who does aerobic exercise for 30 minutes a day work out with weights about four times a week to improve endurance and strength. -Julia Indik, MD, assistant professor of medicine, Sarver Heart Center, University of Arizona, Tucson

Yoga instructor

I teach movement based on kriya yoga, which is the practice of physically slowing down while moving through postures. It's a way of calming the mind and connecting with the body without fighting against it the way that a highly intense aerobic exercise does.

A 30-minute practice would entail at least five to seven minutes of deep, rhythmic inhaling and exhaling, bringing attention to the quality of your breath. Prolonging the exhalation is key to bringing about a meditative mind. Follow this with gentle floor stretches, holding them for as long as it is comfortable.

If you want a more energetic practice, you can move through a very easy combination of movements called sun salutations. This is a series of postures that works many parts of the body — from your muscles to your cardiovascular and nervous systems — in a well-rounded, concise set of poses. I recommend doing sun salutations for 10 to 15 minutes and then moving to the floor for some grounding stretches, like a seated forward bend, seated twists, or hip openers. Doing these toward the end of the practice helps you regain calming energy and soothe some of the intensity of the sun salutations. -Mia Taylor, president and founder, yogalearningcenter.com, Pleasant Hill, California